1. Field of Invention
This invention relates to railroad car trucks and more particularly to an improved connection between a side frame and a bolster of said truck.
2. Prior Art
A modern railroad car truck forming part of a railroad car is commonly referred to as a 3-piece truck in that a pair of spaced side frames resiliently carry a transversely positioned bolster. End portions of the bolster are positioned in windows in each side frame to form a loose connection therebetween. This connection includes sets of coil springs to provide vertical cushioning of the bolster which in turn support a body of the railroad car thereabove.
To dampen vertical oscillating inherent with coil spring suspension, each bolster end portion is formed with a pair of pockets which contain friction shoes. The friction shoes in turn interact with wear plates fastened to spaced vertical columns defining in part the side frame windows. The amount of dampening provided by the friction shoes may be constant or variable depending upon whether or not a spring on which the shoe is supported is compressed by the vertical movements of the bolster. In either case, the spring forces the shoe upwardly against a sloped guide surface to push the shoe outwardly to contact the side frame window wear plate. This contact assists in maintaining the side frame and bolster in a squared relationship as well as providing frictional dampening.
Where the frictional engagement between the shoe and side frame window wear plate is constant, the bolster may be formed with outwardly projecting pair of vertical gibs on each side of the friction shoe windows. The gibs engage with end walls of the side frame column to limit bolster rotation. When side frame-bolster rotation occurs, the window columns are duly stressed to cause deformation of the columns.
Where the frictional engagement between the shoe and side frame window wear plate is variable, the wear plate extends beyond the friction shoe pocket. During bolster rotation, engagement between the wear plate and lands formed on the bolster on each side of the friction shoe pocket can occur. This engagement limits bolster rotation but also causes side frame window column deformation.